it‘s+adj+to do 和it+adj+to do sth 有什么用法

1、It is important to drink enough water every day.it形式主语，没有意思的，to drink enough water every day真正主语，意思是：每天喝足够的水很重要。为了句子平衡，使用了形式主语，而把真正主语放在后面，所以句型：it‘s+adj+to do的意思是：做某事怎么样。

2、Doctors think it is important to drink enough water every day.这时候It is important to drink enough water every day是宾语从句，作think的宾语。此时，it是形式宾语important为宾语补足语to drink enough water every day为真正宾语。

作逻辑主语

形式主语it作为形式主语的it并无实际语义，只是为满足语法上的需要，避免句子头重脚轻，它代替的是句子的逻辑主语，概括起来会有如下情况：

不定式作逻辑主语

如：It is very kind of you to give me a hand in time.

It is my pleasure to address the meeting.

从句作逻辑主语

如：It is so happened that the tickets were sold out.

It is extremely obvious that she has been lying about her identity.

首先，要说明一下，这是find加附加成分的用法：
it‘s+adj+to do 是做主语从句
it+adj+to do sth 是宾语从句
所以，第一个it是形式主语
第二个it是形式宾语
例句：I find it is easy to study well
I find it easy to study well

1.It's happy to play some ball games.
2.It's interesting to watch films.
3.It is easy to answer this question.
4.It is important to learn English well!

1 It is important to drink enough water every day.
it形式主语，没有意思的，to drink enough water every day真正主语，意思是：每天喝足够的水很重要。你看，主语那么长，而谓语就is important 那么短，是不是头重脚轻啊，为了句子平衡，使用了形式主语，而把真正主语放在后面，所以句型：it‘s+adj+to do 的意思是：做某事怎么样。
2 Doctors think it is important to drink enough water every day.
这时候It is important to drink enough water every day.
是宾语从句，作think的宾语。因为think 可以形成think+ 宾语+宾语补足语，所以此句可改成Doctors think it important to drink enough water every day.
也就是少了be动词is.此时，it是形式宾语
important为宾语补足语to drink enough water every day为真正宾语。
能这样用的，除了find外，常见的还有：find,believe等